Preparation of vanadium antimonate based catalysts using SnO2 ·xH2 O

ABSTRACT

A method of preparing a catalyst having the elements and the proportions indicated by the following empirical formula: 
     
         VSb.sub.m A.sub.a D.sub.d O.sub.x 
    
     where 
     A is one or more Ti, Sn, where Sn is always present 
     D is one or more Li, Mg, Ca, Sr, Ba, Co, Fe, Cr, Ga, Ni, Zn, Ge, Nb, Zr, Mo, W, Cu, Te, Ta, Se, Bi, Ce, In, As, B, Al and Mn wherein 
     m is 0.5 to 10 
     a is greater than zero to 10 
     d is zero to 10 
     x is determined by the oxidation state of the cations present, 
     comprising making an aqueous slurry of a mixture of source batch materials comprising compounds of said elements to be included in the final catalyst, followed by drying and heat calcining the mixture to an active catalyst, wherein the source batch material for the tin is a solution which comprises SnO 2 .xH 2  O wherein x≧0 dispersed in tetraalkyl ammonium hydroxide wherein the tetraalkyl ammonium hydroxide is defined by the following formula: 
     
         C.sub.n H.sub.2n+1 NOH 
    
     wherein 
     5≧n≧1, 
     drying said slurry and calcining the mixture to an upper calcination temperature of at least 500° C.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a method for the preparation of tin-containingvanadium-antimony oxide catalysts useful for the catalytic ammoxidationof C₃ to C₅ paraffins or olefins, more specifically for the preparationof catalysts for the ammoxidation of propane or isobutane or propyleneor isobutylene to its corresponding α,β-unsaturated mononitrile,acrylonitrile or methacrylonitrile. In addition, the catalyst may beused in the ammoxidation of methylpyridine, m-xylene or the oxidation ofo-xylene to cyanopyridine, isophthalonitrile or phthalic anhydride,respectively.

More specifically, the invention relates to the use of a SnO₂.xH₂ Owherein x≧0 dispersed in a solution of a tetraalkyl ammonium hydroxideas the reagent for tin in the preparation of catalysts containingvanadium and antimony and tin in oxide form. These types of catalystsare disclosed for instance in U.S. Pat. Nos. 3,681,421, 4,788,317,5,008,427 and in British specifications 1,336,135 and 1,336,136,published in November 1973.

Not all sources of tin are equally effective as promoters invanadium-antimony oxide catalysts for the oxidation and ammoxidation ofsaturated C₃ and C₄ alkanes, particularly ammoxidation. In fact, U.S.Pat. No. 5,214,016 and EPO 691306-A1 teach that the source of tinpromoter is critical to the performance characteristics of the finishedcatalyst. It is believed that the tin should be present in very finelydivided form in the precursors of such catalysts in order for the tin tobe fully reactive when the solid state reaction takes place uponcalcination of the catalyst precursor mixture. Tin oxide sol is asuitable source in making catalysts of the present invention; see U.S.Pat. No. 5,008,427. However, ground tin oxide or tin oxide made byreacting tin metal with nitric acid are decidedly less effective sourcesin catalyst preparation. While current commercially available tin oxidesol is effective, it has a serious disadvantage because it is a veryexpensive source.

SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a method of making asuperior oxidation (particularly ammoxidation) catalyst while avoidingthe use of current commercially available tin oxide sols.

It is another object of the invention to make such a catalyst at afraction of the expense with respect to the tin component as compared tousing current commercially available tin oxide sol as the source of tinin the catalyst precursor.

Other objects, as well as aspects, features and advantages, of theinvention will become apparent from a study of the specificationincluding the specific examples.

The foregoing and other objects are accomplished by the presentinvention according to which there is provided a method of making acatalyst containing vanadium, antimony and tin in the oxide state whichcomprises making an aqueous slurry of a mixture of source batchmaterials comprising compounds of the elements to be included in thefinal catalyst, followed by drying and calcining the mixture to form anactive catalyst, wherein the source batch material for the tin is asolution which comprises SnO₂.xH₂ O wherein x≧0 dispersed in tetraalkylammonium hydroxide wherein the tetraalkyl ammonium hydroxide is definedby the following formula:

    (C.sub.n H.sub.2n+1).sub.4 NOH

wherein

5≧n≧1.

Preferably, tetramethyl ammonium hydroxide is utilized in the practiceof the invention.

The catalyst can be made from any suitable organic or inorganicprecursor compounds of V and Sb, and compounds used to introduce otheroptional elements into the final catalyst after calcination, as is wellknown in the art, such as the salts, oxides, hydroxides ormetallo-organic compounds of such elements, with the tin beingintroduced to the batch of raw materials for preparing such catalysts inthe form of a solution of SnO₂.xH₂ O dispersed in tetraalkyl ammoniumhydroxide as previously disclosed herein. The batch mixture of precursormaterials is heated and calcined in a known manner until the finalcatalyst results. Examples of such raw source batch materials are ofcourse shown in the specific working examples herein.

Particularly effective procedures for the manufacture of the catalystare set forth in U.S. Pat. Nos. 4,784,979, 4,879,264, 3,860,534 and5,094,989, herein incorporated by reference. In addition, the catalystmay optionally be treated by one or more of the methods disclosed inU.S. Pat. Nos. 5,432,141 and 5,498,588, also herein incorporated byreference.

In making the catalysts of the present invention, the upper calciningtemperature is usually at least 500° C., but for ammoxidation ofparaffins this temperature is preferably over 750° C., most often atleast 780° C.

The catalyst may be unsupported or supported on a suitable carrier.Preferably the catalyst is supported on a carrier such as silica,alumina, silica alumina, zirconia or mixtures thereof.

A preferred method of the invention is to make catalysts having theelements and the proportions indicated by the empirical formula:

    VSb.sub.m A.sub.a D.sub.d O.sub.x

where

A is one or more Ti, Sn, where Sn is always present

D is one or more Li, Mg, Ca, Sr, Ba, Co, Fe, Cr, Ga, Ni, Zn, Ge, Nb, Zr,Mo, W, Cu, Te, Ta, Se, Bi, Ce, In, As, B, Al and Mn wherein

m is 0.5 to 10

a is greater than zero to 10

d is zero to 10

x is determined by the oxidation state of the cations present,

which comprises making an aqueous slurry of a mixture of source batchmaterials comprising compounds of said elements to be included in thefinal catalyst, followed by drying and heat calcining the mixture to anactive catalyst, wherein the source batch material for the tin is asolution which comprises SnO₂.xH₂ O wherein x≧0 dispersed in tetraalkylammonium hydroxide wherein the tetraalkyl ammonium hydroxide is definedby the following formula:

    (C.sub.n H.sub.2n+1).sub.4 NOH

wherein

5≧n≧1,

drying said slurry and calcining the mixture to an upper calcinationtemperature of at least 780° C. The upper calcination temperature can beup to 1200° C., but is most often not over 1050° C.

In another aspect of the present invention, there is provided a processfor making an α,β-unsaturated mononitrile selected from acrylonitrileand methacrylonitrile, by the catalytic reaction in the vapor phase of aparaffin selected from propane and isobutane with molecular oxygen andammonia and optionally a gaseous diluent, by catalytic contact of theforegoing reactants in a reaction zone with a catalyst, the feed to saidreaction zone containing a mole ratio of said paraffin to NH₃ in therange from 2.5 to 16 (preferably 4 to 12; especially preferred being 5to 11) and a mole ratio of said paraffin to O₂ in the range from 1 to 10(preferably 2 to 9, especially preferred being 3 to 9), said catalysthaving the empirical composition recited in the last previous paragraph,said catalyst having been made by the method of the last previousparagraph.

The catalyst may also be used in the ammoxidation of methylpyridine andm-xylene to cyanopyridine and isophthalonitrile or the oxidation ofo-xylene to phthalic anhydride. The mole ratios of NH₃ to methylpyridineand O₂ to methylpyridine are 1 to 5 and 1 to 10, respectively. The moleratios of NH₃ to m-xylene and O₂ to m-xylene are 1 to 5 and 1 to 10,respectively. In the phthalic anhydride reaction, the ratio of O₂ too-xylene may range from 1 to 10.

The catalyst prepared by the process of the present invention may alsobe utilized in the ammoxidation of propylene or isobutene with ammoniaand oxygen to produce acrylonitrile or methacrylonitrile. The mole ratioof NH₃ to olefin may range from about 1 to 5 and the mole ratio of O₂ toolefin may range from 1 to 10 in this reaction under conventionaltemperatures and conditions well known in the art.

DETAILED DESCRIPTION OF THE INVENTION

The following examples of making the catalysts and the ammoxidationreactions using the catalysts so made are exemplary only and should notbe understood to be in any way limiting.

EXAMPLE 1

A catalyst having the composition VSb₁.4 Sn₀.2 Ti₀.1 O_(x) (Catalyst No.17388-79) was prepared by mixing 27.30 g of V₂ O₅ powder with a solutionconsisting of 100 ml of 30% H₂ O₂ in 900 ml of water in a two literbeaker. After reaction of the V₂ O₅ powder was complete, 61.25 g of Sb₂O₃ was added followed by 2.40 g of TiO₂ powder (Degussa P-25). Thebeaker was covered with a watch glass and the mixture was stirred andheated for about 3 hours. In a separate beaker, 10.13 g of SnO₂.xH₂ O("acid tin oxide" Magnesium Elektron Inc., received Jun. 7, 1991) wereadded to 100 ml of water and 8 ml of 25 wt % solution of tetramethylammonium hydroxide. The mixture was heated on a hot plate with constantstirring until a translucent mixture formed. This tin-containingdispersion was then added to the foregoing vanadium, antimony, titaniumdispersion. The mixture was stirred in an uncovered beaker with heatingin order to reduce the volume by evaporation of water. When the mixturecould no longer be stirred, it was dried in an oven at 120° C.Thereafter, it was calcined for 1 hour at 325° C. then for 8 hours at650° C., then cooled and crushed and sieved and the 20-35 mesh particlescollected. A portion of this was calcined for 3 hours at 820° C. then at650° C. for an additional 3 hours.

The calcined catalyst was then contacted with isobutanol using about6.25 ml of isobutanol per gram of catalyst by placing the catalyst in acoarse glass frit funnel, pouring the isobutanol over the catalyst,stirring the catalyst in the isobutanol in order to spread the catalystevenly over the bottom of the funnel, then allowing the isobutanol topass through the funnel without suction. This washing was done a totalof three times. After the last of the isobutanol was passed through thefunnel, the catalyst was heated in an oven at 120° C. to remove theresidual isobutanol on the catalyst.

The catalyst was evaluated for ammoxidation of propane using a 1/4titanium U-tube fixed bed reactor. The gaseous feed to the reactor had amolar ratio of 3 propane/1 ammonia/2 oxygen/5 nitrogen at 15 psigpressure. At a reactor temperature of 490° C. and a contact time of 1.4seconds, selectivity to acrylonitrile was 61.2% at a propane conversionof 19.2%. At a reactor temperature of 495° C. and a contact time of 1.4seconds, selectivity to acrylonitrile was 58.6% at a propane conversionof 21.2%.

EXAMPLE 2

A catalyst having the composition VSb₁.4 Sn₀.2 Ti₀.1 O_(x) was preparedby mixing 27.30 g of V₂ O₅ powder with a solution consisting of 100 mlof 30% H₂ O₂ in 900 ml of water in a two liter beaker. After reaction ofthe V₂ O₅ powder was complete, 61.25 g of Sb₂ O₃ was added followed by2.40 g of TiO₂ powder (Degussa P-25). The beaker was covered with awatch glass and the mixture was stirred and heated for about 3 hours. Ina separate beaker, 10.13 g of SnO₂.xH₂ O ("acid tin oxide" MagnesiumElektron Inc., received Jun. 7, 1991) were added to 100 ml of water and30 ml of 25 wt % solution of tetramethyl ammonium hydroxide. The mixturewas heated on a hot plate with constant stirring until a translucentmixture formed. This tin-containing dispersion was then added to theforegoing vanadium, antimony, titanium dispersion. The mixture wasstirred in an uncovered beaker with heating in order to reduce thevolume by evaporation of water. When the mixture could no longer bestirred, it was dried in an oven at 120° C. Thereafter it was calcinedfor 1 hour at 325° C., then for 8 hours at 650° C., then cooled andcrushed and sieved and the 20-35 mesh particles collected. A portion ofthis was calcined for 3 hours at 820° C. then at 650° C. for anadditional 3 hours.

The calcined catalyst was then contacted with isobutanol using about6.25 ml of isobutanol per gram of catalyst by placing the catalyst in acoarse glass frit funnel, pouring the isobutanol over the catalyst,stirring the catalyst in the isobutanol in order to spread the catalystevenly over the bottom of the funnel, then allowing the isobutanol topass through the funnel without suction. This washing was done a totalof three times. After the last of the isobutanol was passed through thefunnel, the catalyst was heated in an oven at 120° to remove theresidual isobutanol on the catalyst.

The catalyst was evaluated for ammoxidation of propane using a 1/4"titanium U-tube fixed bed reactor. The gaseous feed to the reactor had amolar ratio of 3 propane/1 ammonia/2 oxygen/5 nitrogen at 15 psigpressure. At a reactor temperature of 495° C. and a contact time of 2.4seconds, selectivity to acrylonitrile was 55.6% at a propane conversionof 13.1%.

What is claimed is:
 1. A method of making a vanadium antimony oxidecatalyst containing tin in the oxide state comprising making an aqueousslurry of a mixture of source batch materials comprising compounds ofthe elements to be included in the final catalyst, drying the mixture,and calcining the mixture to form an active catalyst, wherein the sourcebatch material for the tin is a solution which comprises SnO₂.xH₂ Owherein x≧0 dispersed in tetraalkyl ammonium hydroxide, wherein thetetraalkyl ammonium hydroxide is defined by the following formula:

    (C.sub.n H.sub.2n+1).sub.4 NOH

wherein 5≧n≧1.
 2. The method of claim 1 wherein the SnO₂.xH₂ O isdispersed in tetramethyl ammonium hydroxide.
 3. The process of claim 1wherein the calcination is at a temperature of at least 500° C.
 4. Theprocess of claim 3 wherein the calcination temperature is at least 750°C.
 5. The process of claim 3 wherein the calcination temperature is atleast 780° C.
 6. The method of claim 1 wherein the catalyst is supportedon an inert carrier.
 7. The method of claim 6 wherein the carrier isselected from the group consisting of silica, alumina, silica-alumina,zirconia or mixtures thereof.